Hydroxyapatite from Natural Sources for Medical Applications

The aim of this work is to study the physical-chemical, mechanical, and biocompatible properties of hydroxyapatite obtained by hydrothermal synthesis, at relatively low temperatures and high pressures, starting from natural sources (Rapana whelk shells), knowing that these properties influence the behavior of nanostructured materials in cells or tissues. Thus, hydroxyapatite nanopowders were characterized by chemical analysis, Fourier-transform infrared spectroscopy (FT-IR), dynamic light scattering (DLS), scanning electron microscopy (SEM), and X-ray diffraction (XRD). In vitro studies on osteoblast cell lines (cytotoxicity and cell proliferation), as well as preliminary mechanical tests, have been performed. The results showed that the obtained powders have a crystallite size below 50 nm and particle size less than 100 nm, demonstrating that hydrothermal synthesis led to hydroxyapatite nanocrystalline powders, with a Ca:P ratio close to the stoichiometric ratio and a controlled morphology (spherical particle aggregates). The tensile strength of HAp samples sintered at 1100 °C/90 min varies between 37.6–39.1 N/mm². HAp samples sintered at 1300 °C/120 min provide better results for the investigated mechanical properties. The coefficient of friction has an appropriate value for biomechanical applications. The results of cell viability showed that the cytotoxic effect is low for all tested samples. Better cell proliferation is observed for osteoblasts grown on square samples.     

Chronic health conditions and school performance among children and youth

PurposeChronic health conditions are common and increasing among U.S. children and youth. We examined whether chronic health conditions are associated with low school performance.MethodsThis retrospective cohort study of 22,730 children and youth (grades 2–11) in San Jose, California, was conducted from 2007 through 2010. Health conditions were defined as chronic if reported in each of the first 2 years, and school performance was measured using standardized English language arts (ELA) and math assessments.ResultsChronic health conditions were independently associated with low ELA and math performance, irrespective of ethnicity, socioeconomic status, or grade level. Adjusted odds ratios for the association between any chronic health condition and low (“basic or below”) performance were 1.25 (95% confidence interval [CI], 1.16–1.36; P < .001) for ELA and 1.28 (95% CI, 1.18–1.38; P < .001) for math, relative to students without reported health conditions. Further adjustment for absenteeism had little effect on these results. The strongest associations were found for ADHD, autism, and seizure disorders, whereas a weak association was found for asthma before but not after adjusting for absenteeism, and no associations were found for cardiovascular disorders or diabetes.ConclusionsChronic neurodevelopmental and seizure disorders, but not cardiovascular disorders or diabetes, were independently associated with low school performance among children and youth.     

The effect of midterm peer feedback on student functioning in problem-based tutorials

Within Problem-Based Learning successful learning depends on the quality of cognitive, social and motivational contributions students make to the tutorial group. But at the same time, not all students in PBL automatically contribute in a high quality manner, which might impede successful group functioning. This study investigated whether peer process feedback combined with goal setting can be used to improve the quality of students’ individual contributions. A mixed-methods explanatory design, in which 74 second-year Health Sciences students participated, combined a pre- and posttest with a focus group. The results indicated that the quality of the contributions only increased for students with a below average score on the pre-test. The qualitative data confirmed that the impact of the feedback could be increased by combining individual reflection by means of goal setting with face-to-face discussion. Another suggestion is to investigate whether midterm peer process feedback is more effective for first year students, because they are still developing their tutorial behavior, as opposed to second year students.